The present invention relates to an improved process of washing spherical particles, for example sol-gel spheres of uranium, to remove the organic layer adhering to such spheres with an aqueous solution of a surface active substance.
In the preparation of metal and metal oxide spheres such as uranium and the salts thereof, a customary technique to form substantially spherical particles is to disperse an aqueous metal sol into an organic phase, such as kerosene or carbon tetrachloride, such that under dispersing conditions the aqueous phase droplets solidify in the organic phase, the aqueous phase being substantially or completely immiscible with the organic phase. The dispersed droplets of the sol become spherical in shape due to their inherent surface tension in the dispersed state within the immiscible organic liquid. The spheres so produced usually have an organic film adhering to the outside surface of the sphere and it is to the removal of this film that the present invention is directed.
It should also be mentioned that during the sphere formation in the organic liquid it has been proposed to add a surfactant to the organic liquid itself in order to prevent the aqueous-phase droplets from coalescing with each other and to maintain the droplets in the dispersed state. This procedure is described in U.S. Pat. No. 3,586,742.
In both instances it is usually necessary to wash the spheres with water to remove soluble salts of the gel or hydroxide material that are formed along with the spherical particles.
Previous procedures to accomplish the above objectives include the following: After globule or spherical particle formation in a relatively viscous organic phase, the particles were separated and washed with petroleum ether and subsequently eluted with a watery phase. In some cases residues of petroleum ether caused problems. For this reason, washing with petroleum ether was sometimes followed by a re-rinsing operation with methanol. After washing with methanol, the final washing operation, in this case, was performed with a watery rinsing phase. It will be apparent then that this procedure is not only difficult but adds to the cost of manufacture.
Another process that has been proposed is regeneration of the organic phase. Forming oils can in some cases be regenerated by contacting the oil with an adsorbing bed, the adsorbing bed collecting decomposition products of the oil. Decomposition products of the forming oil have in the past sometimes continued adhering to the globules, thus interfering with the elution.